One of the key elements to combat climate change is
understanding what forcing are behind. Many people are aware of the numerous
human activities that contribute to climate change but not very many have a
grasp on the natural processes that also cause our climate to change. All
possible climate change causes need to be taken into account when trying to
figure out if the changes we are seeing are natural and if they are not, how to
combat them at the source.
Some of the natural processes that have been causing our
climate to change over the past 4 and a half billion years have been our
distance from the sun (orbital cycle), the suns strength, earths reflectivity
(albedo), and greenhouse gas emissions (GHG emissions). Each of these have
occurred in constant cycles throughout our history but one in particular, GHG
emissions, has been amped up with advances in technology by humans. We know this by looking at proxies of past
climate change that allow us to measure the relative amounts of GHGs in the
atmosphere at different time periods.
The reason we can know that none of the other climate change
causes are causing our climate to change is because of the time scales that
they work on. Orbital cycles occur at very regular intervals. The earth rotates
around the sun in an ellipse type path that grows and stretches as times goes
on. When it comes to affecting climate change though, these changes happen over
a span of thousands of years and are too long to account for the changes we see
from them.
Similarly to the changes in our orbit, the sun has also been
getting steadily brighter and hotter. This though has been happening since the
earth first formed and would not account for the sudden increase that we have
seen in average global temperatures in the fast few decades. The sun goes
through a sun spot cycle as well but that happens every 11 years.
Earth reflectivity has been changing throughout time as well
and controls how much energy from the sun is radiated back out into space. If
albedo is high, more energy is reflected back into space, if it low, more
energy is absorbed. Many things affect albedo such as particles in the
atmosphere, ice sheets on the poles, and the different structures or plants
that occupy different land areas. If we have more ice masses and reflective aerosols
in the atmosphere, more incoming solar radiation is reflected and the earth
cools. But if ice melts and leaves fresh soil exposed or trees are cut down for
fields that exposed more dirt, these things can cause our albedo to go down and
our temperature to rise. This can also cause a negative feedback because more
ice melting causes more soil to be exposed and warmed by incoming radiation.
This warmed soil causes more ice to melt and so on and so forth.
Lastly we have GHG emissions. These emissions have steadily
been increasing since the existence of humans. Before our time, these gases
were emitted by volcanoes and wild fires. Since nothing was able to control
these processes we can and say that they occur at somewhat frequent times
throughout history. What we can’t ignore though is that there has been an
increase in the presence of these gases in the past few decades. The only
factor that has differed through their semi-constant occurrences is humans. We
have essentially sped up the process of GHG emissions into the atmosphere way
beyond something we have ever seen in the past thousands of years.
